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At least 325 records · Page 18

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NASA NTRS1972

LEED structures due to interaction of CO and O2 with /0001/ and /1,0,-1,0/ Re at 20 C to 920 C.

Clean Re surfaces were produced by the Ar(+) ion bombardment technique. Results reported previously by Farnsworth and Zehner (1969) for the adsorption of CO and molecular oxygen on the (0001) Re surface were confirmed. The exposure of a (0001) Re surface to CO at elevated crystal temperatures produced no additional structures. Neither increased surface defect densities nor excitation of the adsorbate enhanced the adsorption characteristics of CO or molecular oxygen on the surfaces studied.

Zehner, D. M.↗

NASA NTRS1971

Electric contact phenomena in ultra clean and specifically contaminated systems.

Contact resistance has been used to characterize the processes of physical contact in metallic systems with ultraclean surfaces. The contact resistance versus load curves of iron and two cobalt alloys were used to demonstrate the existence of surface work hardening and interfacial creep during contact as well as the fracture characteristics of an interfacial junction as the load is removed. The presence of an adsorbed film of hydrogen or hydrogen ions on iron completely changes the contact process. A comparison of the contact resistance versus load data for ultrapure iron, and iron-cobalt alloy, and a cobalt molybdenum-chromium was used to illustrate the effect of substrate mechanical properties on static adhesion and the ability to convert these data for the estimation of the dynamic coefficient of friction under the particular experimental conditions.

Keller, D. V., Jr.↗

NASA NTRS1973

Potassium food supplement

Potassium gluconate is considered best supplementary source for potassium. Gluconate consistently received highest taste rating and was indistinguishable from nonsupplemented samples. No unfavorable side effects were found during use, and none are reported in literature. Gluconate is normal intermediary metabolite that is readily adsorbed and produces no evidence of gastrointestinal ulcerations.

Bourland, C. T.↗

NASA NTRS1973

Zeta potential control for electrophoresis cells

Zeta potential arises from fact that ions tend to be adsorbed on surface of cell walls. This potential interfaces with electric field sensed by migrating particles and degrades resolution of separation. By regulating sign and magnitude of applied potential induced charge can be used to increase or decrease effective wall zeta potential.

Fogal, G. L.↗

NASA NTRS1973

Gas chromatography of volatile organic compounds

System has been used for problems such as analysis of volatile metabolities in human blood and urine, analysis of air pollutants, and in tobacco smoke chemistry. Since adsorbent is reusable after porper reconditioning, method is both convenient and economical. System could be used for large scale on-site sampling programs in which sample is shipped to central location for analysis.

Zlatkis, A.↗

NASA NTRS1973

Estimating sorber capacity for multiple contaminants

Computer program estimates quantity of activated charcoal required to control multiple contaminants. Program scans all contaminants by potential parameter value and then orders them from lowest to highest values. It calculates quantity of sorbent required to remove most strongly adsorbed material; and then, using potential plot data, capacity of other materials is calculated on basis of corrected capacity.

Olcott, T. M.↗

NASA NTRS1972

Use of LEED, Auger emission spectroscopy and field ion microscopy in microstructural studies

Surface research tools such as LEED, Auger emission spectroscopy analysis, and field ion microscopy are discussed. Examples of their use in studying adhesion, friction, wear, and lubrication presented. These tools have provided considerable insight into the basic nature of solid surface interactions. The transfer of metals from one surface to another at the atomic level has been observed and studied with each of these devices. The field ion microscope has been used to study polymer-metal interactions and Auger analysis to study the mechanism of polymer adhesion to metals. LEED and Auger analysis have identified surface segregation of alloying elements and indicated the influence of these elements in metallic adhesion. LEED and Auger analysis have assisted in adsorption studies in determining the structural arrangement and quantity of adsorbed species present in making an understanding of the influence of these species on adhesion possible. These devices are assisting in the furtherance of understanding of the fundamental mechanism involved in the adhesion, friction, wear, and lubrication processes.

Ferrante, J.↗

NASA NTRS1972

Surface properties of thermionic electrodes

A quasi-equilibrium model which provides semiquantitative predictions of the oxygen reaction with refractory metals was developed at high temperature and low pressure. Extensive experimental data was obtained on adsorption and work function properties for a wide variety of adsorbates (Cs, K, Na, I, Br, Cl, and O) on several refractory metals (W, Ta, Mo, and Re). Conclusions and recommendations for research on alkali metal adsorption, oxygen adsorption, and adsorption of cesium - oxygen mixtures are included.

Stickney, R. E.↗

NASA NTRS1973

Atmosphere control

Atmospheric control studies emphasized the carbon dioxide problem. Trace contaminants are removed by solid adsorbents and by catalytic oxidation. Humidity control and storage systems for atmospheric constituents are briefly summarized.

Jones, W. L.↗

NASA NTRS1972

Problems affecting the fidelity of pressure measuring instruments for planetary probes

Determination is made of the nature and magnitude of surface-related effects that cause errors in pressure measuring instruments, with special reference being made to instruments intended for use in planetary probes. The interaction of gases with clean surfaces of metals likely to be used as gage construction materials was studied. Special emphasis was placed on the adsorption, chemical reaction, and electron-induced desorption processes. The results indicated that all metals tested were subject to surface processes which would degrade gage fidelity. It was also found, however, that the formation of inert adsorbed layers on these metal surfaces, such as carbon on platinum, greatly reduced or eliminated these effects. This process, combined with a system design which avoids contact between reactive gases and hot filaments, appears to offer the most promising solution to the gage fidelity problem.

Hudson, J. B.↗

NASA NTRS1973

Atom beam surface interaction studies: Experimental system development

Quantitative deposition by standard techniques of adsorbates containing C and Si onto selected substrates is studied. The interaction kinetics of a beam of oxygen, nitrogen, or hydrogen atoms of known flux are investigated by Auger electron spectroscopy and LEED. Desborbed molecules will be analyzed by mass spectroscopy using modulated beam techniques. Experimental conditions permitting, two sets of measurements will be correlated.

Gregory, J. C.↗

NASA NTRS1972

Evaluation of spacecraft toxic gas removal agents

A study of the decomposition of various compounds adsorbed on charcoal was made, with a view toward providing a critical appraisal of previous data from charcoal adsorption studies. It was found that thermal decomposition occurs at temperature lower than previously suspected during the charcoal stripping process. A discussion is presented dealing with the various types of reactions found. A rough, quantitative scheme for correcting previous analytical results is developed and presented.

Source record↗

NASA NTRS1973

Electrical properties of dry rocks

The mechanism by which atmospheric moisture affects the conductivity and dielectric constant of rock specimens was studied in time and frequency domains. It is suggested that adsorbed water molecules alter the surface conductivity in a manner similar to that observed in semiconductors and insulators. Powdered basalts show a low-frequency dispersion produced by the atmospheric moisture remaining in the pore system of the sample in a high vacuum; this effect is attributed to isolated adsorption centers. Simulated lunar permafrost at 100 K and a vacuum of 10 to the -8th power torr together with data on lunar samples contaminated with atmospheric moisture and the dielectric properties of ice at various temperatures indicate that, if permafrost exists in the moon it should present a relaxation peak at approximately 300 Hz; for temperatures up to 263 K it may go up to 20 KHz. It is concluded that in order to have electrical steady state conditions in rock samples it is necessary to have volume charge accumulations at interfaces within the sample and at the electrode sample interface. A method for measuring heterogeneous dielectrics with non-negligible ohmic and dielectric conductivities is proposed and experimentally verified.

Morrison, H.↗

NASA NTRS1973

Odor intensity and characterization studies of exhaust from a turbojet engine combustor

Sensory odor tests of the exhaust from a turbojet combustor operating at simulated idle conditions were made by a human panel sniffing diluted exhaust gas. Simultaneously, samples of undiluted exhaust gas were collected on adsorbent substrates, subsequently removed by solvent flushing, and analyzed chemically by liquid chromatographic methods. The concentrations of the principal malodorous species, the aromatic (unburned fuel-related) and the oxygenated (partially burned fuel) fractions, as determined chromatographically, correlated well with the intensity of the odor as determined by sniffing. Odor intensity increased as combustion efficiency decreased. Combustor modifications which increased combustion efficiency decreased odor intensity.

Butze, H. F.↗

NASA NTRS1972

Physisorption of argon on pyrex at low pressures.

Equilibrium pressures, numbers of argon atoms adsorbed per unit area and the DR parameters are given for argon adsorption on Pyrex for pressures ranging from 0.625 nanotorr to 12.7 microtorr at 77, 81.4, 87.8 and 90 K. Physical adsorption isotherms, Dubinin-Radushkevich plots, and isosteric heat curves are also given for argon on Pyrex.

Jen, J. S.-C.↗

NASA NTRS1972

Lunar atmosphere measurements.

Cold cathode ionization gauges were left on the lunar surface during Apollo missions 14 and 15 to measure the amount of lunar gas. The observed nighttime concentration is very low, about 200,000 per cu cm, which is less than the neon concentration that might be expected from the solar wind. This suggests that the lunar surface is not saturated with solar wind neon, and hence that less neon is being released from the surface than impinges upon it. The low nighttime concentration shows that contaminant gases from the Apollo operations freeze out at night or become adsorbed on the cold lunar surface. Observed daytime concentrations have been two orders of magnitude greater than the nighttime values and appear to be due mainly to contamination in the landing area. The rate at which the contamination is decreasing is characterized by a time constant of a few months. Gas clouds have been seen at times and these appear to have been released from Apollo hardware left on the lunar surface.

Johnson, F. S.↗

NASA NTRS1972

Some surface characteristics and gas interactions of Apollo 14 fines and rock fragments.

Comprehensive survey of the physical surface characteristics of Apollo 14 fines, two fragments of a breccia (14321), and a crystalline rock (14310). The survey was carried out with optical and both scanning and transmission electron microscopy and by studying the adsorption of a variety of gases including nitrogen, hydrogen, and water vapor. Our objective in the optical microscope study was to relate the visible geological and petrological features to the surface properties. Electron microscopy particularly helped relate surface roughness and particle fusion to gas adsorption and pore structure. The fine sample (14163,111) had a surface area of 0.210 sq m/g and a helium density of 2.9 g/cc. Similar values have been observed with breccia fragments. Other observations include physical adsorption of molecular hydrogen at low temperatures and of water vapor at ambient temperatures. It is concluded that these particular lunar materials, while capable of adsorbing water vapor, do not retain it for any significant time at low pressures, nor, under lunar conditions, is there any indication of absorption or penetration.

Cadenhead, D. A.↗

NASA NTRS1972

Cryogenic applications for environment simulation.

Some of the applications of cryogenics for simulating space environmental conditions are reviewed, and typical existing space simulation facilities are described. The techniques of adapting cryogenics to environmental simulation are discussed. Special attention is given to cryosorption pumps designed to accelerate cryogenic cooling of the adsorbent material.

Hardgrove, W. F.↗